use std::fs::File;

type Result<T> = std::result::Result<T, Box<std::error::Error>>;

struct Foo {}

impl Foo {
    fn example_fn(name: &str) -> Result<File> {
        match File::open(name) {
            Ok(v) => Ok(v),
            Err(e) => Err(Box::new(e)),
        }
    }
}

fn main() -> Result<()> {
    // ...
    Ok(())
}

#[test]
fn test() {
    use super::Foo;

    let result = Foo::example_fn("foo.txt");

    assert!(/* verify Err(std::io::Error(Simple(std::io::ErrorKind::NotFound))) was received */ );
}